Replying to Flipping

Ok so, i had been wanting to do a flip on skis forever and I was telling my friend and he can do a flip on the ground(I can't) andhe said that you have to be able to do one the ground (and it's easier) in order to do one on skis. Your opinions: do you have to be able to do a flip on the ground to do on skis.? If you can do a flip on skis, can you do one on the ground( for those who can flip on skis). Finally which is easier? this is referring to front flips. I've managed to land one on skis and still can't do one on the ground. Thanks